1. Field of Invention
The present invention relates to a combination projectile ram depth and orientation gauge which is operatively insertable into a breech area of a cannon/gun tube. (the terms cannontube and guntube are used interchangeably herein; cannontube is used henceforth for brevity). More specifically, the invention relates to a gauge for measuring (1) the depth of the projectile inside the cannontube bore after the projectile has been rammed and seated into the lands and grooves of the rifling of the cannontube with respect to the cannontube face and (2) any angular deviation of orientation of the seated projectile from its normal position with respect to the centerline of the breech chamber and the cannontube.
2. Description of the Prior Art
Artillery weapons in the past have typically been area weapons which deliver their munitions in a general area with no pinpoint accuracy or precision. However, today's artillery has taken advantage of the advances in technology, whereby the weapons are becoming more accurate with surgical precision capabilities and are not simply area weapons. With current investigations directed in making area weapons into extremely accurate pieces, it is understandable why much effort is being devoted to make this conversion. Much of this investigative effort is directed to the interior ballistics of the powder chamber and to the seating of the projectile. The difference of the rammed depth of the projectile may increase or decrease the interior volume of the effective powder chamber and consequently the muzzle velocity of the projectile. This ultimately effects accuracy of the terminal ballistics and point of impact of the projectile.
The firing of a field artillery cannon requires several operational steps to insure its safety and performance during use, especially during investigative and scientific test firing of the cannon. One such safety test is to measure the depth of the projectile inside the cannontube bore after the projectile has been rammed and seated in the lands and grooves of the rifling of the cannontube. This measurement is done to insure that the projectile's rotating band is engraved into the rifling grooves with sufficient depth to prevent a fall-back or a blow-by condition. The fall-back condition means the projectile is not sufficiently rammed and seated in the rifling grooves. This condition allows the projectile to fall back away from the rifling grooves and onto the powder charge when the cannontube is elevated. When this condition occurs and the cannon is fired, the projectile is not able to travel down the cannontube. The heated gases from the burning propellent can initiate detonation of the fuse and/or can cause the discharge of the high explosive charge in the projectile. Obviously, this can be a catastrophic situation. Another safety test for measuring the ram depth is the determination that the projectile is seated at a sufficient depth to not only hold the projectile in a rigid position while elevating the cannontube, but to also ensure that the rotating band has engraved sufficiently into the lands and grooves of the rifling to prevent the blow-by condition. The blow-by condition results when the projectile is seated in the rifling just enough to hold it in place but does not completely seal all the voids between the lands and grooves, thus allowing an exit route for the propelling gases from the burning powder charge. This results in a condition known as a sticker. The cannon has fired but the projectile has stuck somewhere in the cannontube. This condition may be catastrophic also, since the projectile is now super heated, very unstable, and may spontaneously detonate.
There is no known prior art publications in the cannontube art relating to gauge devices for the purpose of measuring the ram depth of the seated projectile. Prior to this invention, Applicant used a seating gauge to measure the seated or rammed depth of a projectile in the cannontube bore. This gauge was constructed from wood in a T shape with a short horizontal leg normal to a long vertical leg. The short leg rested against the face of the breech and allowed the long leg to travel into the breech until it touched the base of the projectile. This long leg had a rigid tape measure attached to it and when it touched the base of the projectile it was locked in place with a thumb screw. The gauge was then removed from the cannontube and the ram distance was read from the end of the long leg to the breech side of the supporting leg.
In using this wooden gauge a number of disadvantages have been encountered. For example, it is readily easy for a number of individuals to use the same gauge in the same rammed projectile situation and to obtain different readings. However, with the gauge of the present invention, it is possible at the same setting to derive repeatable and accurate measurements, resulting in consistent and meaningful data acquisition.
3. Specific Prior Art
U.S. Pat. No. 3,780,438, entitled Rifling Lands Inspection Gage and issued Dec. 25, 1973 to Styczynski, discloses a gage for inspecting the lands of a rifled barrel bore for erosion.
U.S. Pat. No. 4,348,812, entitled Gun Barrel Internal Diameter Indicator and issued on Sep. 14, 1982 to Middleton, discloses an indicator or gauge for measuring and checking the internal diameter of a gun barrel.
U.S. Pat. No. 4,982,505, entitled Gauge for Measuring Both the Depth and the Diameter of a Bore Hole and issued on Jan. 8, 1991, discloses a gauge for measuring both the depth and the diameter of a bore hole.
U.S. Pat. No. 5,170,569, entitled Device for Measuring Dimensions to Calculate the Head Space for Guns and issued on Dec. 15, 1992 to Anderson, discloses a device for measuring dimensions to calculate the head space for guns.
4. Statement of the Invention
The combined depth and orientation gauge of the present invention represents an improvement over the known prior art a over the above-mentioned wooden gauge. The gauge of the present invention is used for measuring and verifying two different parameters or dimensions; namely, (1) the depth that the projectile has been rammed and seated into the lands and grooves of the cannontube bore rifling (which engraves into the rotating band of the projectile); this is also known as the seated or rammed depth, with respect to the face of the cannontube or breech area; and (2) the angular deviation measurement of orientation of the seated projectile from its proper position in the center of the bore area of the cannontube, with respect to the cannontube centerline.
The gauge of the present invention improves the accuracy and consistency of readings from round to round and from operator to operator. This is accomplished by consistently centering the gauge in the center of the bore area, by centering the length measurement's contact point on the center of the projectile base, and by eliminating the inconsistent play and slop from using the wooden gauge.
The gauge of the present invention is a combination gauge in that it not only measures the depth of ram of the seated projectile, but also measures the deviation of orientation of the projectile from the normal. Measuring the deviation of the orientation of the projectile is required in order to determine what effect canting of the projectile in the cannontube bore has on accuracy. If the projectile is not perfectly centered and the cannon is fired, the projectile may travel down the cannontube bore in an unorthodox manner, which may have significant effects on the exit orientation of the projectile and eventually terminal accuracy. The present invention solves these problems by measuring both the ram depth of the projectile and the seated orientation of the projectile with a single insertion of the gauge into the cannontube. Further, the measured depth readings and the orientation information are electronically recorded in a data logger and stored and analyzed by a computer.